They will keep. Whenever we served eggs at a banquette or brunch, we held them in steam tables. To keep them fresh we would bring out smaller batches which we refreshed every 15 minutes or so. I don't know If that is a realistic option for you or not.

Per Benny's advice, I don't honestly think a crock is a good tool for this. Personally, I hate buffet lines but you often have to work with that. The steam tray is much preferred for holding the eggs. My concern with using a crockpot is that the eggs would dry out really fast.

imho, and from much experience, I think scrambled eggs only hold at all in a steam table, and even then only for short periods of time. It is necessary to put them out in small batches and have someone in charge of keeping the pan stocked. Otherwise not only will they dry out around the edges, they sometimes even turn an extremely unattractive shade of green.

Have you considered doing poached eggs? You can poach them ahead of time, store them in cold water in the fridge, and then place them in warm water just before serving. How many people are you expecting? Poached eggs are more work than scrambled, but I find that scrambled eggs are one of those foods that should be very fresh to be at their best.

I agree with Pierino that a steam table (or chafer) is preferable. Either of those will spread them out in such a way that the entire pan will hold a temperature, where a crock pot concentrates them in a deep mass where it is much harder to hold a temperature at the center without them seriously overcooking at the perimeters. They need to be held at no lower than 135 degrees. You have a total of 4 hours to cook them, hold them, and serve them.